Definition of biodegradable polymers

In this chapter, we have discussed polymer stmcture at the level of the repeating unit. The repeating unit not only has a specific chemical structure but also acts as the source of interaction at the molecular scale. With respect to this, now we will be introducing the concept of biodegradable polymer blends. A polymer blend is classically defined as a physical mixture of two or more polymers, which occurs on a macro scale. We are now going to also consider the science at molecular/nanometre scales, ie, taking polymer repeating unit into account rather than entire polymer chains. For the purposes of this book, the definition of a polymer blend is as follows ... 

There are many definitions of biodegradability expounded by different authors. One publication [3] defines biodegradable polymer composites as "materials obtained from nature or by synthetic route, whose chemical bonds are cleaved at least in one step by enz5mies from the biosphere." T) ical degradation times for various materials, including biopol5miers and biocomposites, have now been estimated and are shown in Table 10.1. 

Note 2 Usually, degradation results in the loss of, or deterioration in useful properties of the material. However, in the case of biodegradation (degradation by biological activity), polymers may change into environmentally acceptable substances with desirable properties (see Definition 3.1... 

In contrast to many other polymers classified as biodegradable, PVA exhibits a backbone solely made up of carbon. The presence of a heteroatom like O or N in the main chain is definitely not a prerequisite for Nature to handle a polymeric structure that does not exist in nature. PVA degradation starts with random oxidations of the polymer backbone in the extracellular or periplasmic space of some microbes. Specific enzymes able to detect such sites of first attack continue in a hydrolytic way, yielding ever smaller polymer fragments that finally can be metabolised by the microbe or the microbial community. 

Numerous methods to measure the biodegradability of polymers have been developed. Because of slightly different definitions or interpretation of the term biodegradability , the different approaches are therefore not equivalent in terms of information they provide or the practical significance. Since the typical exposure environment involves incubation of a polymer substrate with microorganisms or enzymes, only a limited number of measurements are possible. These include those pertaining to the substrates, to the microorganisms, or to the reactive products. 

Table 1. General definitions of a biodegradable polymer (or plastic) proposed by Standard Authorities ...

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